Bamboo can grow up to 3 feet a day.
It would be nice if they measured it's current growth rate before calculating an age. I bet it's more than "other members of this species". But there's no guarantee that the current growth rate represents this plant's past history either.
What im saying is that every individual of that species grows at 3-10 cm per year. It would be odd if it grew 100 times faster wouldn't it? It would be like some sort of ultra mutant freak plant which had little in common with it's original species.